Mask assembly



FIG. 1 top-front perspective view of a mask assembly showing the new design;

FIG. 2 is a bottom-rear perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a back view thereof;

FIG. 5 is a left side view thereof, the right side view being a mirror image of the left side view;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken lines show portions of a mask assembly which form no part of the claimed design. 

CLAIM The ornamental design for a mask assembly, as shown and described. 